1. Field of the Invention
The present invention relates to a sound reproducer, and more particularly, it relates to a sound reproducer for reproducing sound signals corresponding to a plurality of channels.
2. Description of the Background Art
Television receivers containing various types of surrounding circuits have been increased in recent years. Particularly according to the Dolby surround system (trade mark in the name of Dolby Laboratories Licensing Corporation), the user can enjoy stereophonic sound with feeling of presence at a theater in his own room by reproducing VTR software or video disk software recorded in the Dolby surround system.
In the aforementioned Dolby surround system, however, it is impossible in principle to attain a sound effect absolutely identical to that at a theater.
Japanese Patent Laying-Open Gazette No. 251400/1986 discloses a Pro-Logic surround system (trade mark in the name of Dolby Laboratories Licensing Corporation) which contains a directional enhancement circuit, as an extended system of the aforementioned Dolby surround system. While difference signal components of left and right sound signals are reproduced by rear speakers to attain feeling of presence in the Dolby surround system, localization and the feeling of presence are improved in the Pro-Logic surround system with additional processing of clarifying directivity of the sound. According to this Prologic surround system, the sound is reproduced by front speakers for left, right and center channels and a pair of rear speakers for a surround channel.
FIG. 1 shows the aforementioned Pro-Logic surround system. Referring to FIG. 1, left and right input terminals 1 and 2 are supplied with left and right stereo signals (sound signals) L' and R', which have been encoded in accordance with the Dolby surround system. A first adder 3 adds the right stereo signal R' to the left stereo signal L', to generate a sum signal C' (=L'+R'). A substracter 4 substracts the right stereo signal R' from the left stereo signal L', to generate a difference signal S' (=L'-R'). First and second detectors 5 and 6 detect levels of the left and right stereo signals L' and R' respectively. Third and fourth detectors 7 and 8 detect levels of the sum signal C' and the difference signal S' respectively. A first level ratio detector 9 detects the level ratio of output signals of the first and second detectors 5 and 6. A second level ratio detector 10 detects the level ratio of output signals of the third and fourth detectors 7 and 8.
A VCA (voltage control amplifier) 11 controls the levels of the left and right stereo signals L' and R' in accordance with output signals of the first and second level ratio detectors 9 and 10. A second adder 12 selects the left and right stereo signals L' and R' and one of output signals of the VCA 11, and adds up the same to generate left and right stereo output signals (left and right channel signals) L and R, a center output signal (center channel signal) C and a surround output signal (surround channel signal) S. A center mode control circuit 13 switches the left and right stereo output signals L and R and the center output signal C in accordance with modes. A passive decoder 14 performs signal processing such as delay, noise removal etc. on the surround output signal S.
The aforementioned Pro-Logic surround system has a test mode function, so that the user can readily set volume balance (sound field) between the five speakers in a listening position. In this test mode function, the speakers sequentially regenerate random noise having central frequency at 500 Hz by one to two seconds, so that the user controls the volume balance between the respective speakers.
However, a conventional Pro-Logic surround decoder has no means of clearly displaying which speaker is currently driven at what volume level, and hence it is difficult for the user to correctly control the sound volume.